Abstract

The structure and stability of the dominant lactic acid bacterium population were assessed during wheat flour sourdough type I propagation by using singly nine strains of Lactobacillus sanfranciscensis. Under back-slopping propagation with wheat flour type 0 F114, cell numbers of presumptive lactic acid bacteria varied slightly between and within starters. As determined by randomly amplified polymorphic DNA-PCR and restriction endonuclease analysis-pulsed-field gel electrophoresis analyses, only three (LS8, LS14, and LS44) starters dominated throughout 10 days of propagation. The others progressively decreased to less than 3 log CFU g(-1). Partial sequence analysis of the 16S rRNA and recA genes and PCR-denaturating gradient gel electrophoresis analysis using the rpoB gene allowed identification of Weissella confusa, Lactobacillus sanfranciscensis, Lactobacillus plantarum, Lactobacillus rossiae, Lactobacillus brevis, Lactococcus lactis subsp. lactis, Pediococcus pentosaceus, and Lactobacillus spp. as the dominant species of the raw wheat flour. At the end of propagation, one autochthonous strain of L. sanfranciscensis was found in all the sourdoughs. Except for L. brevis, strains of the above species were variously found in the mature sourdoughs. Persistent starters were found in association with other biotypes of L. sanfranciscensis and with W. confusa or L. plantarum. Sourdoughs were characterized for acidification, quotient of fermentation, free amino acids, and community-level catabolic profiles by USING Biolog 96-well Eco microplates. In particular, catabolic profiles of sourdoughs containing persistent starters behaved similarly and were clearly differentiated from the others. The three persistent starters were further used for the production of sourdoughs and propagated by using another wheat flour whose lactic acid bacterium population in part differed from the previous one. Also, in this case all three starter strains persisted during propagation.

Cell densities (CFU g−1) after sourdough propagation at 30°C for 6 h in 10 subsequent days with use of wheat flour type 0 F114. Data are the means from three independent experiments (n = 3). The center line of each box (□) represents the median; the top and bottom of the box represent the 75th and 25th percentiles of the data, respectively. The tops and bottoms of the error bars represent the 5th and 95th percentiles of the data, respectively. The circles (○) in each box plot extend to the outliers of the data, and very extreme points are represented as individual data points (*). Control, unstarted sourdough. Sourdough (S) started with strain Lactobacillus sanfranciscensis LS3, LS6, LS8, LS12, LS14, LS40, LS41, LS44, or LS48 is indicated.

ΔpH values (difference in pH units between the initial pH and final pH after sourdough propagation at 30°C for 6 h during 10 subsequent days by using wheat flour type 0 F114. Data are the means from three independent experiments (n = 3). The center line of each box represents the median (□); the top and bottom of the box represent the 75th and 25th percentiles of the data, respectively. The top and bottom of the error bars represent the 5th and 95th percentiles of the data, respectively. The circles in each box plot extend to the outliers of the data (○). Control, unstarted sourdough. Sourdough started with Lactobacillus sanfranciscensis LS3, LS6, LS8, LS12, LS14, LS40, LS41, LS44, or LS48 is indicated.